Communications networks use a transmission medium to transmit information in the form of computer data, voice, music, video, etc., from one station to another. The communications medium may be a wired link, a fiber optic link, or a wireless link. The wireless link may include, but is not limited to, radio frequency, infrared, laser light, and microwave. The network may, in fact, use a combination of different types of communications links.
With the exception of a small number of networks that use dedicated communications links between each station, most information networks use a shared transmission medium to carry the transmitted information. Examples of information networks using a shared transmission medium include: Ethernet, token ring, wireless Ethernet (IEEE 802.11), and many proprietary networks.
However, by sharing a communications medium between multiple stations, there are situations that arise when stations are required to wait a significant amount of time before they are able to transmit their data. Additionally, situations exist when simultaneous transmissions from different stations occur and result in the mutual destruction of the transmissions. Such situations are undesirable in providing quality of service (QoS) to multimedia, voice, and data transfers and in making efficient use of scarce spectrum on a wireless medium.
For some applications, such as voice telephony, video tele-conferencing, and other real-time, bidirectional, interactive applications, extended transfer times can severely and rapidly degrade the performance of the applications to a level that is unacceptable. For example, in voice telephony applications, if the delay between one user speaking and another user listening is greater than a few milliseconds, the delay becomes noticeable to the users and the users' satisfaction level for the telephone connection begins to drop.
One way to ensure that applications requiring a low maximum network latency receive the level of service that they require is to implement some form of QoS transfers of data traffic between stations. In many networks with QoS transfers, communications traffic in a network is partitioned into multiple categories and streams. The categories are prioritized while the streams are parameterized according to their specific performance requirements and traffic characteristics. For example, traffic carrying a telephone conversation between two users will be given a higher priority than traffic carrying data for a file transfer between two computers; whereas traffic carrying a teleconferencing video will be parameterized differently from traffic carrying a television video in terms of their data rate and delay requirements. By prioritizing categories and parameterizing streams for the traffic, traffic of higher priority or higher QoS demands receives better service, and hence these networks offer and meet performance guarantees.
However, traffic categories, as implemented in an IEEE 802.11e wireless communications network, provide only a fixed (static) priority for messages in the differing categories. All messages of a given traffic category share a single priority level. Given a fixed number of different traffic categories, it may not be possible to provide the necessary level of prioritization to meet individual QoS demands. A finer level of differentiation between messages is required, and a fixed priority method, such as traffic categories, does not provide the needed flexibility to specify different communications parameters on a message-by-message basis. Additionally, the ability to change, on the fly, a message's parameters as network conditions and requirements change can greatly enhance the network's performance.
A need has therefore arisen for a methodology that permits the specification of various communications parameters on a message-by-message basis and the exchange and negotiation of the communications parameters between communicating stations as dictated by performance needs and bandwidth availability.